(CBS News) The massive explosion near Waco, Texas, that leveled buildings for blocks around and which could be heard dozens of miles away was so powerful because of the materials involved, City University of New York physics professor Michio Kaku explained on "CBS This Morning."

"Let's put this in respective: The Boston bombing, as tragic as it was, released the energy of one stick of dynamite. An ammonia nitrate, released in an accident of this sort, can release the energy of several truckloads of dynamite, enough to set off a 2.1-magnitude earthquake in terms of intensity. The Oklahoma City bombing, for example, was based on one ton of fertilizer. Here, they were licensed to have over 25 tons. So you can imagine the scale, the enormity of what happened.

Ammonia nitrate is set off in two ways: "Ammonia nitrate added with fuel oil can set off a tremendous fertilizer explosion and here we think there was anhydrous ammonia (in gas form), which can be set off with water," Kaku explained.

"The working hypothesis is there was a fire explosion. Firemen were called on site in a routine operation, but the hose water might have set off anhydrous ammonia, creating a chain reaction of explosions, releasing this ... force, which can level several city blocks."

This case, Kaku said, may be cause to "rewrite the book" on environmental regulations. He explained, "The (Environmental Protection Agency) regulations say it's OK to have this amount of material because nothing's going to happen, but there's a rare sequence of events, the right pressure, temperature, and right amount of water will set off anhydrous ammonia."

"Fertilizer explosions are some of the worst ever in the history of this country," Kaku said. "In 1947, 2,000 tons of ammonium nitrate detonated, killing 600 people, also in Texas."